A number of catalytic processes have been developed for the preparation of dimethyltin dichloride by the reaction of tin metal with methyl chloride.
Hoye et. al. in U.S. Pat. No. 3,415,857 describes the use of onium salts as catalysts for the preparation of dialkyltin dihalides from tin metal and an alkyl halide. His catalyst system consists of a stannous or organotin chloride or bromide in addition to the onium salt in approximately equimolar amounts and optionally a metal other than tin. The reaction times are usually greater than 12 hours and yields range from moderate to poor. In fact, reasonable yields are only obtained when the catalyst residue is recycled as in Examples 10 and 11.
Molt et. al. in U.S. Pat. No. 3,519,665, discloses the use of tetraalkylphosphonium or tetraalkylammonium iodides as catalysts for the preparation of dialkyltin dichlorides from tin metal and an alkyl chloride. Because iodides are expensive, it becomes necessary to distill the product in order to recover the catalyst residues for re-use. Moreover, yields of dialkyltin dichlorides are generally poor.
Witman et. al. in U.S. Pat. No. 3,857,868, reported that quarternary ammonium salts are effective catalysts for preparing dimethyltin dichloride from tin metal and methyl chloride provided that the reaction is run under constant pressure, at least 60 psi, and in the presence of a solvent. To maintain constant pressure throughout the reaction, methyl chloride must be fed into the system periodically.
Knezevic et. al., in U.S. Pat. No. 3,901,824, discloses the use of a two-component catalyst system for the preparation of dimethyltin dichloride from tin metal and methyl chloride. The catalyst system consists of: (a) tin tetrachloride; and, (b) a trihydrocarbylamine, a trihydrocarbylphosphine, a tetraalkylammonium chloride, or a tetraalkylphosphonium chloride.